The present invention relates to an apparatus for preparing electrophotographic photosensitive members, comprising a step of coating a coating solution formed by mixing two or more kinds of charge-generating materials.
Lamination type photosensitive members obtained by laminating a charge transport layer and a charge generation layer chiefly comprised of a charge-generating material have been already put into practice use as electrophotographic photosensitive members employing organic photoconductive materials. In such photosensitive members, it is possible to suitably select charge-generating materials to obtain a photosensitive members having desired spectrum sensitivities, but, when it is intended to obtain photosensitive member having a photosensitive wavelength region which is wide to a certain extent (i.e., being panchromatic), it is known to mix two or more kinds of charge-generating materials having different photosensitive wavelength regions, as disclosed in U.S. Pat. No. 3,992,205, U.S. Pat. No. 4,026,704, etc. In this instance, two or more kinds of charge-generating materials are simultaneously mixed in a binder resin and a solvent, or separately dispersed therein, followed by mixing of such materials to obtain a charge generation layer coating solution, and this solution is then coated on a substrate to form a charge generation layer.
In the instance where the electrophotographic photosensitive members are prepared with use of such a charge generation layer coating solution simultaneously containing two or more kinds of charge-generating materials, there occurs a problem as follows: The problem occurs because the mixing ratio of the respective charge-generating materials in the coating solution may change with the lapse of time because of differences in the dispersed particle size, dispersibility and agglomeration properties depending on the individual charge-generating material. This problem after tends to occur especially when using a coating medium tank comprising a filter provided in a feeding system for the charge generation layer coating solution for the purpose of removing foreign matters included in the coating process, dust inclusions from the atmosphere, coarse particles agglomerated, etc.
Under such circumstances, it is impossible to prepare photosensitive members having always constant electrophotographic properties. Accordingly, the mixing ratio of the charge-generating materials must be measured to effect feedback to a coating apparatus, but this is unsuitable for the continuous production of photosensitive members because such measurement is too time consuming.